In a traditional solar panel, solar cells are electrically interconnected in strings using thin flat conductive interconnect “ribbons” or “tabs”. The solar cells may be crystalline silicon or thin film solar cells including amorphous silicon, CIGS, and CdTe. The ribbons are typically thin copper strands that may be coated with a tin or solder alloy such as tin-silver, tin-lead, tin-lead-silver, or bismuth-tin.
In one convention design, the front of the first solar cell in a string is electrically connected to the back of the second solar cell in the string, the front of which is electrically connected to the back of the third solar cell, and so on using pairs of spaced interconnect ribbons soldered to the cells. Strings of solar cells, in turn, are electrically connected by bus ribbons. A typical panel may also include a glass cover sheet and a weather protective back plastic sheet.
Back contact solar cells were engineered to reduce shadowing losses and the like. See Van Kerschaver and Beaucerne, “Back-Contact Solar Cells: A Review”, Progress in Photovoltaics: Research and Applications, 2006; 14:107-123 (2005). Solland Solar, for example, offers back contact solar cells called “Sunweb” where the back contacts are in an array. Another back contact design has the contacts in an interdigitated design.
In this way, the back sheet of the panel can include a foil conductive layer to electrically interconnect solar cells in a string.